Modeling superheated steam vacuum drying of wood

A two-dimensional mathematical model developed for vacuum-contact drying of wood was adapted to simulate superheated steam vacuum drying. The moisture and heat equations are based on the water potential concept whereas the pressure equation is formulated considering unsteady-state mass conservation...

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Bibliographic Details
Published in:Drying technology 2004-01, Vol.22 (10), p.2231-2253
Main Authors: Defo, M, Fortin, Y, Cloutier, A
Format: Article
Language:English
Subjects:
Acer saccharum
Air velocity
drying curve
equations
Evaporative heat flux
Heat and mass transfer coefficients
heat transfer
mass transfer
mathematical models
Radiant heat
superheated steam vacuum drying
Vacuum drying
wood
wood drying
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Summary:A two-dimensional mathematical model developed for vacuum-contact drying of wood was adapted to simulate superheated steam vacuum drying. The moisture and heat equations are based on the water potential concept whereas the pressure equation is formulated considering unsteady-state mass conservation of dry air. A drying test conducted on sugar maple sapwood in a laboratory vacuum kiln was used to infer the convective mass and heat transfer coefficients through a curve fitting technique. The average air velocity was 2.5 m s −1 and the dry-bulb temperature varied between 60 and 66°C. The ambient pressure varied from 15 to 11 kPa. Simulation results indicate that heat and mass transfer coefficients are moisture content dependent. The simulated drying curve based on transfer coefficients calculated from boundary layer theory poorly fits experimental results. The functional relation for the relative permeability of wood to air is a key parameter in predicting the pressure evolution in wood in the course of drying. In the case of small vacuum kilns, radiant heat can contribute substantially to the total heat transfer to the evaporative surface at the early stages of drying. As for conventional drying, the air velocity could be reduced at the latter stage of drying with little or no change to the drying rate.
ISSN:0737-3937
1532-2300
DOI:10.1081/DRT-200039984